A method object is not a function and cannot be invoked as a function.
Various mechanisms in the object system take a method object and invoke its method
function, as is the case when a generic function is invoked. When this
occurs it is said that the method is invoked or called.

A method-defining form contains the code that is to be run when the
arguments to the generic function cause the method that it defines to
be invoked. When a method-defining form is evaluated, a method object
is created and one of four actions is taken:

Each method has a specialized lambda list, which determines
when that method can be applied. A specialized lambda list is like
an ordinary lambda list except that a specialized parameter
may occur instead of the name of a required parameter. A specialized parameter
is a list (variable-nameparameter-specializer-name),
where parameter-specializer-name is one of the following:

denotes a parameter specializer which satisfies the type specifier(eql object), where object is the
result of evaluating form. The form form is evaluated in
the lexical environment in which the method-defining form is evaluated.
Note that form is evaluated only once, at the time the method is
defined, not each time the generic function is called.

Given a generic function and a set of arguments, an applicable
method is a method for that generic function whose parameter
specializers are satisfied by their corresponding arguments. The
following definition specifies what it means for a method to be
applicable and for an argument to satisfy a parameter specializer.